X-ray analysis of samples is a growing area of interest across many industries such as medical, pharmaceutical, and petroleum. The use of x-ray fluorescence, x-ray diffraction, x-ray spectroscopy, x-ray imaging, and other x-ray analysis techniques has led to a profound increase in knowledge in virtually all scientific fields.
X-ray fluorescence (XRF) is an analytical technique by which a substance is exposed to a beam of x-rays to determine, for example, the presence of certain components. In XRF, at least some of the elemental constituents of the substance exposed to x-rays can absorb x-ray photons and produce characteristic secondary fluorescence. These secondary x-rays are characteristic of the elemental constituents in the substance. Upon appropriate detection and analysis these secondary x-rays can be used to characterize one or more of the elemental constituents. XRF techniques have broad applications in many chemical and material science fields, including industrial, medical, semiconductor chip evaluation, petroleum, and forensics, among others.
As some examples of measurements required in the petroleum industry, trace levels of contaminants in petroleum feedstocks is a notorious problem in petroleum refining. Sulfur is a common component in crude oil streams—and its removal from final product is mandated due to its impact on the environment, as regulated by the US EPA under the Clean Air Act. Sulfur is harmful to the environment, and the cost of its removal is high. Therefore, monitoring sulfur levels early in the refining process is important. Chlorine and vanadium contaminants are considered “bad actors” by the refining industry for primarily non-regulatory, process control reasons. Chlorides also pose one of the greatest problems to the refining industry. According to a 2005 paper by The National Association of Corrosion Engineers (“NACE”): “Recently, an increasing number of refineries have experienced extreme corrosion and fouling in crude distillation unit overheads and/or naphtha hydrotreating units. The root causes were traced to severe spikes in the chloride levels.”
U.S. Pat. Nos. 6,934,359 and 7,072,439, hereby incorporated by reference herein in their entirety and assigned to X-Ray Optical Systems, Inc., the assignee of the present invention, disclose monochromatic wavelength dispersive x-ray fluorescence (MWD XRF) techniques and systems for the analysis of liquid samples. Moreover, commonly assigned U.S. Pat. No. 7,277,527 (also included by reference in its entirety) entitled “MOVABLE TRANSPARENT BARRIER FOR X-RAY ANALYSIS OF A PRESSURIZED SAMPLE” addresses a particular problem inherent in moving sample streams in such systems as discussed further below.
As one particular example of a measurement system for such contaminants, the above-incorporated patents disclose techniques for the determination of the level of elements in petroleum fuels, and a commercialized analyzer (SINDIE) is now in widespread use for, e.g., sulfur measurement at petroleum refining, pipeline, and terminal facilities.
XRF fluid testing can take place off-line, i.e., using a bench-top, laboratory-type instrument to analyze a sample. The material is removed from its source (e.g., for fuel, from a refinery or transportation pipeline) and then simply deposited in a sample chamber; or into a windowed sample cell which is then deposited into a chamber. Off-line, bench-top instruments need not meet any unusual operational/pressure/environmental/size/weight/space/safety constraints, but merely need to provide the requisite measurement precision for a manually-placed sample. Moreover, off-line instruments can be easily maintained between measurements.
In contrast to off-line analysis, on-line analysis provides “real-time” monitoring of sample composition at various points in the manufacturing process. For example, all fuel products are subject to sulfur level compliance—requiring some variant of on-line monitoring during fuel refining and transportation in pipelines. On-line analysis of fuels in a refinery and in pipelines, however, requires consideration of numerous operational issues not generally present in an off-line, laboratory setting. A fully automated fuel sample handling system is required—with little or no manual intervention or maintenance. Also, since fluids are usually under pressure in pipelines, any sample handling system must account for pressure differentials. This is especially important since certain portions of XRF x-ray “engines” (discussed further below) operate in a vacuum. Also, the instrument's electronics require packaging in an explosion-proof housing—separate from the sample handling system.
In an on-line analyzer for crude and heavy fuel applications, differing sample stream viscosities make it challenging to present samples to the analyzer at a stable pressure and flow rate. Chlorine measurement presents another challenge because the chlorine mostly exists in water phase, which may not mix homogeneously in crude.
In these applications one of the most critical components is the sample barrier(s) which allow photons of the x-rays to excite sulfur atoms in the fluid, and photons emitted from the atoms to be counted at the engine's detector, while at the same time maintaining the vacuum in the x-ray engine and the pressure of the fluid. X-ray stimulation may create sulfur (or other hard element) ionization and adsorption at this interface over time and on certain types of barrier materials—leading to undesired sulfur residue and degradation of the barrier's x-ray transparency. More generally, many XRF applications require a barrier to protect the engine from any number of adverse interface effects from the sample material and/or the measurement environment.
The barrier system of above-incorporated U.S. Pat. No. 7,277,527 offered a very important and successful solution to these problems in the form of a moveable barrier advanced at programmable intervals to clean portions of a window roll, however, it is still desirable to provide techniques which keep this interface clean, and the sample stream moving through the sample cell at a desirable rate and consistency.
What is required, therefore, are lower cost and lower maintenance sample handling techniques for an on-line x-ray analysis system handling high viscosity samples, which protects the x-ray engine from adverse sample and environmental effects, while maintaining the integrity and transparency of the interface to the sample for accurate measurements without excessive moving parts.